Olfactory discrimination byHeteropsylla cubana (Homoptera: Psyllidae) between susceptible and resistant species ofLeucaena (Leguminosae).

In the field, adult psyllids,Heteropsylla cubana Crawford, oriented significantly more towards the caged seedlings of susceptibleLeucaena leucocephala (Lam.) de Wit than to those of the resistant tree species,Leucaena collinsii Britton & Rose, or the nonhostAmaranthus spinosus L. In a dual-choice bioassay using a still-air olfactometer, the females demonstrated a strong positive response to the hexane extract ofL. leucocephala leaves at 1×10(-3) g equivalents (g eq) of leaf material. The females did not orient to leaf extracts ofL. collinsii at high concentrations but responded positively at a lower concentration of 1×10(-4) g eq. Olfactory discrimination byH. cubana between resistant and susceptible host species should be considered in selection and breeding programs.

Clinical pharmacokinetic study of tiazofurin administered as a 1-hour infusion.

Tiazofurin, 2-beta-D-ribofuranosylthiazole-4-carboxamide, is cytotoxic to murine and human tumor cells. In earlier Phase-I/-II trials performed in other centers in patients with solid tumors, the drug was given mainly as a 10-min bolus or as a continuous i.v. infusion for 5 days. These protocols were associated with serious side effects, including neurotoxicity, pleuropericarditis, and occasional myelosuppression. In our study, 26 patients with end-stage leukemia were treated with tiazofurin with 1-hr daily i.v. infusions, resulting in lower incidence and less severity of side effects. In this group, 7 attained complete remission and 7 showed hematologic responses. Out of 12 evaluable patients with myeloid blast crisis of chronic granulocytic leukemia, 10 (83%) responded to therapy, with 6 attaining complete response. We present pharmacokinetic parameters of our clinical study and examine some of the reasons for the lower toxicity found in our trials. In leukemic patients during and after infusion at doses of 1,100, 2,200 and 3,300 mg/m2 tiazofurin peak plasma concentrations were 245, 441 and 736 microM, respectively, values one-half of those calculated from other reports with a 10-min bolus administration. In our 1-hr infusion method, biphasic pharmacokinetics were noted with alpha t1/2 and beta t1/2 of 0.5 and 6.2 hr, and tiazofurin was eliminated at a faster rate than in previous trials with continuous infusion. The area under the curve with our 1-hr infusion was 52% of that reported for the same dose given by continuous infusion. Our 1-hr infusion method and prompt and effective treatment of side effects enabled us to administer higher doses and larger total amounts of tiazofurin in longer treatment cycles than in any previous trials elsewhere. Tiazofurin therapy using 1-hr infusion may be feasible for other carefully selected types of malignancies.

Down-regulation of c-myc and c-Ha-ras gene expression by tiazofurin in rat hepatoma cells.

There was an overexpression of the c-myc gene (11-fold) and of the c-Ha-ras gene (2-fold) in rat hepatoma 3924A cells compared to normal rat liver as measured by dot-blot analysis of total cytoplasmic RNA. The overexpression of c-myc was attributed to a 10- to 14-fold amplification and rearrangement of the c-myc sequences as determined by Southern blot analysis. The expression of the c-myc also was dependent upon the proliferative state of the hepatoma cells. Tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide; NSC 286193), an inhibitor of the activity of IMP dehydrogenase (EC 1.1.1.205), the rate-limiting enzyme of GTP biosynthesis, resulted in a rapid drop (less than 1 h) to 50% of control in the target enzyme activity in the hepatoma cells and in a subsequent marked decrease to 55% in GTP concentration. These events were followed at 12 h of tiazofurin treatment by a 3-fold reduction in the expression of the c-myc gene and a 9-fold decline in that of the c-Ha-ras gene. These results in the hepatoma cells provide evidence in support of the earlier demonstrated correlation in K562 cells between GTP concentration and expression of c-myc and c-ras genes (Olah et al., 1989). These genes might depend on GTP for their expression in hepatoma cells and they might cooperate in a signal pathway that controls cell proliferation.

Biochemically directed therapy of leukemia with tiazofurin, a selective blocker of inosine 5'-phosphate dehydrogenase activity.

Tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide, NSC 286193), a selective inhibitor of the activity of IMP dehydrogenase (EC 1.1.1.205), the rate-limiting enzyme of de novo GTP biosynthesis, provided in end stage leukemic patients a rapid decrease of IMP dehydrogenase activity and GTP concentration in the blast cells and a subsequent decline in blast cell count. Sixteen consecutive patients with end stage acute nonlymphocytic leukemia or myeloid blast crisis of chronic granulocytic leukemia were treated with tiazofurin. Allopurinol was also given to inhibit xanthine oxidase activity to decrease uric acid excretion and to elevate the serum concentration of hypoxanthine, which should competitively inhibit the activity of hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8), the salvage enzyme of guanylate synthesis. Assays of IMP dehydrogenase activity and GTP concentration in leukemic cells provided a method to monitor the impact of tiazofurin and allopurinol and to adjust the drug doses. In this group of patients with poor prognosis, five attained a complete hematological remission and one showed a hematological improvement. A marked antileukemic effect was seen in two other patients. All five evaluable patients with myeloid blast crisis of chronic granulocytic leukemia reentered the chronic phase of their disease. Five patients with acute nonlymphocytic leukemia were refractory to tiazofurin and three were unevaluable for hematological effect because of early severe complications. Responses with intermittent 5- to 15-day courses of tiazofurin lasted 3-10 months. Tiazofurin had a clear antiproliferative effect, but the pattern of hematological response indicated that it appeared to induce differentiation of leukemic cells. In spite of toxicity with severe or life-threatening complications in 11 of 16 patients, tiazofurin was better tolerated in most patients than other antileukemic treatment modalities and provided a rational, biochemically targeted, and biochemically monitored chemotherapy which should be of interest in the treatment of leukemias and as a paradigm in enzyme pattern-targeted chemotherapy.

Clinical and molecular impact of inhibition of IMP dehydrogenase activity by tiazofurin.

The impact of tiazofurin on inhibition of IMP dehydrogenase was discussed at the clinical and molecular levels. 1. Evidence was provided for the role of IMP dehydrogenase and guanylates in the expression of the neoplastic program in cancer cells with particular relevance to human leukemic cells. 2. The argument for expecting an impact of tiazofurin in human myelocytic cells was provided. 3. Similarity of the kinetics of human leukemic cell IMP dehydrogenase to the rat hepatoma enzyme was documented. 4. New evidence was provided for the role of salvage in chemotherapy and the function of hypoxanthine in inhibiting guanine salvage. 5. The action of tiazofurin and retinoic acid was reported in HL-60 leukemic cells. 6. The effect of tiazofurin and retinoic acid on proliferation and cytotoxicity was outlined for hepatoma 3924A cells. 7. The effect of guanine on induced differentiation by tiazofurin and retinoic acid was examined. 8. Biochemical basis was provided for the lack of development of resistance in patients treated with tiazofurin. 9. Presumptive evidence was provided that tiazofurin treatment induced differentiation of leukemic cells in the patients. 10. The molecular biology of tiazofurin-induced differentiation in K-562 cells was reviewed with the possible relevance to clinical treatment that tiazofurin might also act through down-regulation of ras oncogene.

Substituted ergolines: potential antipsychotics with unique profile. II. Neurochemical characterization.

A series of lumilysergol and lysergol derivatives were studied with a number of neurochemical methods. The compounds investigated showed heterogenous profiles on receptor binding tests. They were mostly active on D-2 receptors, but some alpha-1, alpha-2 and 5-HT-2 affinity could also be demonstrated. None of the drugs showed remarkable D-1 activities tested on basal and DA-stimulated adenylate cyclase (AC) enzyme in vitro. On the basis of the effects of the drugs on the mouse whole brain monoamine neurotransmitter and metabolite levels and neurotransmitter biosynthesis rates along with the receptor binding data we conclude that their actions are mainly related to the central dopaminergic system(s). The 2-halo-lumilysergole derivatives were less potent than the 2-halo-lysergoles with respect to their dopaminergic actions. We found the substitution at position 8 to be substantial to achieve agonistic or antagonistic properties, and, interestingly, 2,8-dihalo-lysergoles have proven to be DA agonists. The neurochemical findings are in good agreement with the behavioral results presented in the accompanying paper. We confirmed the behavioral data in that there are two subgroups among 2-halo-lysergoles possessing antipsychotic activity with opposite effects on DA receptors.

Enzyme-pattern-targeted chemotherapy with tiazofurin and allopurinol in human leukemia.

The hypothesis was tested that the increased IMP dehydrogenase activity in human myelocytic leukemic cells, and along with it guanylate biosynthesis, might be a sensitive target to chemotherapy by tiazofurin. 1. IMP dehydrogenase activity in normal leukocytes was 3.1 +/- 0.5 (means +/- S.E.) nmol/hr/mg protein and in leukemic cells it was elevated 15- to 41-fold. The activity of guanine phosphoribosyltransferase in normal leukocytes was 389 +/- 27 nmol/hr/mg protein and in the leukemic cells it increased 2.8- to 6.8-fold. 2. IMP dehydrogenase was purified 4,900-fold to homogeneity from rat hepatoma 3924A with a yield of 30%. The kinetic properties of the hepatoma enzyme were similar to those of the enzyme in human myelocytic leukemic blast cells because of the similarity of the Km's for IMP (23 microM), NAD (44 and 65 microM); the Ki for TAD was 0.1 microM in both enzymes. 3. There was a selectivity of the in vitro response to tiazofurin in human normal and leukemic leukocytes. When labeled tiazofurin was incubated with leukocytes from normal, healthy volunteers and from leukemic patients, the leukemic leukocytes made 20- to 30-fold more TAD and the GTP content decreased as compared to normal leukocytes. This procedure proved to be a suitable predictive test in a clinical setting because patients with positive tests responded to tiazofurin whereas those with negative ones did not. 4. The National Cancer Institute approved a chemotherapeutic phase I/II trial which concentrates on treatment of refractory acute myelocytic leukemia. Tiazofurin is infused in a 60-minute period with a pump to insure uniform delivery. A novel aspect of the trial was that it was directed primarily by the biochemical impact of tiazofurin on IMP dehydrogenase activity and GTP concentration and the tiazofurin doses were to be adjusted accordingly. Patients received allopurinol as a routine precaution against possible accumulation of uric acid in the kidney. 5. In the first eight patients, there was one complete remission, two entered the chronic phase, two entered into partial remission, one did not respond, and two were not evaluable. In the five patients who responded, there was a rapid, profound decrease in IMP dehydrogenase activity of the blast cells and a gradual decline in GTP concentrations. The blast cell count followed the decrease in the GTP concentration. The white blood cell count was largely preserved. 6. Bone marrow aspirates and peripheral blood samples showed that with tiazofurin treatment there was an induced differentiation of the myelocytes.(ABSTRACT TRUNCATED AT 400 WORDS)

Hematological and biochemical action of tiazofurin (NSC 286193) in a case of refractory acute myeloid leukemia.

A patient with refractory acute myeloid leukemia was treated with tiazofurin, an agent that causes inhibition of tumor cell proliferation by depressing GTP concentrations in the malignant cells. The initial dose of 1100 mg/m2 was ineffective clinically and biochemically. Dose escalations to 1650, 2200, and finally 3300 mg/m2 resulted in a marked decrease in the absolute number of blasts without causing bone marrow hypoplasia or marked neutropenia. The decrease in the peripheral blast cell count was observed subsequent to a decline in GTP concentrations in the leukemic cells to less than 30% of the pretreatment value. Consecutive bone marrow examinations showed a remarkable shift from myeloblasts to more mature myeloid elements, suggesting an in vivo differentiative action of tiazofurin. Although a total dose of 23,650 mg/m2 was administered over a 13-day period, only very mild side effects were noted. The absence of complications reported by others in Phase I trials with tiazofurin may be related to our slow administration of the drug by pump over a 1-h period in this trial. Tiazofurin appears to be a promising agent in the treatment of leukemia because of its selective action on leukemic cells and the availability of a rapid in vitro method capable of predicting sensitivity of leukemic cells to the agent and monitoring its activity during treatment by measuring thiazole-4-carboxamide adenine dinucleotide and GTP concentrations. These observations are being tested in a larger group of leukemic patients.

Further studies on the biochemical characterization of the MC-29 virus derived transplantable hepatoma (VTH). II. Modification of cyclic adenosine-3',5'-monophosphate levels by catecholamines, glucagon and Vinca alkaloids in normal chicken liver and VTH.

Basic and stimulated intracellular cAMP concentrations were measured in normal chicken liver and MC-29-virus-derived transplantable hepatoma (VTH) slices after in vitro incubation. Data indicated the preservation of catecholamine receptor but a loss of glucagon receptor in VTH. Comparing the relative stimulatory action of various catecholamines on cAMP concentration it was concluded that as in normal liver a predominantly beta 2-adrenergic receptor exists in the VTH, but its response to adrenaline is greater. Vinca alkaloids induced higher cAMP concentration in VTH than in normal liver. This stimulation was abolished by glucagon, while catecholamines and Vincristine acted in a synergistic manner on cAMP concentration.

Presence of GABA receptors in rat oviduct.

A low concentration of high-affinity, saturable and specific [3H]GABA binding sites has been identified in a membrane fraction of rat oviduct. The specific binding of [3H]GABA was displaced by unlabelled GABA, muscimol and bicuculline. Furthermore in oviductal slices, GABA and a known GABA receptor agonist, i.e. muscimol, produced a significant elevation of cyclic AMP levels, which could be antagonized by GABA receptor blockers, i.e. picrotoxin and bicuculline. The present results indicate that GABA receptors may have a functional significance in rat oviduct.

Bicuculline-sensitive GABA receptors in rat ovary.

A specific [3H]GABA binding site, characterized by a kinetic constant of 52 nM and by a maximal binding capacity of 17 fmol/mg protein was identified in a membrane preparation of rat ovary. [3H]GABA binding was displaced by muscimol, unlabelled GABA or bicuculline. The accumulation of cyclic AMP in the slices of rat ovary was strongly increased by GABA or muscimol and these effects were antagonized by picrotoxin or bicuculline. Our data suggest a possible role of GABA receptors in the regulation of ovarian function in the rat.